This invention relates to medical ultrasonic diagnostic systems, and, in particular, to a fully integrated hand-held ultrasonic diagnostic instrument.
As is well known, modem ultrasonic diagnostic systems are large, complex instruments. Today""s premium ultrasound systems, while mounted in carts for portability, continue to weigh several hundred pounds. In the past, ultrasound systems such as the ADR 4000 ultrasound system produced by Advanced Technology Laboratories, Inc., assignee of the present invention, were smaller, desktop units about the size of a personal computer. However, such instruments lacked many of the advanced features of today""s premium ultrasound systems such as color Doppler imaging and three dimensional display capabilities. As ultrasound systems, have become more sophisticated they have also become bulkier.
However, with the ever increasing density of digital electronics, it is now possible to foresee a time when ultrasound systems will be able to be miniaturized to a size even smaller than their much earlier ancestors. The physician is accustomed to working with a hand-held ultrasonic scanhead which is about the size of an electric razor. It would be desirable, consistent with the familiar scanhead, to be able to compact the entire ultrasound system into a scanhead-sized unit. It would be further desirable for such an ultrasound instrument to retain as many of the features of today""s sophisticated ultrasound systems as possible, such as speckle reduction, color Doppler and three dimensional imaging capabilities.
In accordance with the principles of the present invention, a diagnostic ultrasound instrument is provided which exhibits many of the features of a premium ultrasound system in a hand-held unit. These premium system features are afforded by a digital signal processor capable of performing both greyscale and Doppler signal processing including their associated filtering, compression, flash suppression and mapping functions, as well as advanced features such as synthetic aperture formation, multiple focal zone imaging, frame averaging, depth dependent filtering, and speckle reduction. In particular, the processor provides power Doppler imaging data through use of Hartley transformation and wall filtering to calculate the Fourier power spectrum. In preferred embodiments the digital signal processor is formed on a single integrated circuit chip. This sophisticated ultrasound instrument can be manufactured as a hand-held unit weighing less than five pounds.
A new signal processing algorithm and architecture for Directional Doppler Power Imaging is presented with this invention. This algorithm is based on a concept of transforming the Doppler data after wall-filtering into the Hartley domain. Since Hartley transformation can be embedded in the wall-filtering process, Doppler power of the forward and the reverse flow components can be computed with very little processing overhead. Excluding the computation required for wall-filtering, for an ensemble of N echoes in Doppler sensing, Directional Doppler power can be computed with 2N MULTIPLIES and 4N+1 ADDS operations per pixel that is much more efficient than any existing methods. As a comparison, 6N-4 MULTIPLIES AND 4N-5 ADDS operations are required per pixel if autocorrelation method is used. To appreciate the processing efficiency, it is noted that 2N MULTIPLIES and 2N-1 ADDS operations are required per pixel to calculate the Doppler power alone. Due to simplicity of signal processing, the implementation is very low cost and is suitable for low-power VLSI implementation in a handheld ultrasound imaging system.
The invention has particular applicability in cardiac applications since flow direction and power can be computed simultaneously, rather than separately as in conventional directional power doppler. Direction of flow is obtained directly by integration of the power spectrum below and above the transmitted ultrasound frequency. This allows the imaging of regurgitant flow in the heart valve due to leaks. The imaging can be trans thoracic, trans esophagus, or by catheter to the heart. Because of the speed of the new processing algorithm, imaging limited to the cardiac cycle is feasible and practical.